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<title>Problem 1579. -- [Usaco2009 Feb]Revamping Trails -- 衡阳八中OJ离线版-2012-02-29</title><center><h2>1579: [Usaco2009 Feb]Revamping Trails</h2><span class=green>Time Limit: </span>10 Sec&nbsp;&nbsp;<span class=green>Memory Limit: </span>64 MB<br><span class=green>Submit: </span>738&nbsp;&nbsp;<span class=green>Solved: </span>195<br>[<a href='submitpage.php?id=1579'>Submit</a>][<a href='problemstatus.php?id=1579'>Status</a>][<a href='bbs.php?id=1579'>Discuss</a>]</center><h2>Description</h2><div class=content>每天,农夫John需要经过一些道路去检查牛棚N里面的牛. 农场上有M(1<=M<=50,000)条双向
泥土道路,编号为1..M. 道路i连接牛棚P1_i和P2_i (1 <= P1_i <= N; 1 <= P2_i<= N).
John需要T_i (1 <= T_i <= 1,000,000)时间单位用道路i从P1_i走到P2_i或者从P2_i
走到P１_i

他想更新一些路经来减少每天花在路上的时间.具体地说,他想更新K (1 <= K <= 20)条路经，
将它们所须时间减为０．帮助FJ选择哪些路经需要更新使得从１到N的时间尽量少.

</div><h2>Input</h2><div class=content>* 第一行: 三个空格分开的数: N, M, 和 K

* 第2..M+1行: 第i+1行有三个空格分开的数：P1_i, P2_i, 和 T_i

</div><h2>Output</h2><div class=content>* 第一行: 更新最多Ｋ条路经后的最短路经长度．</div><h2>Sample Input</h2>
			<div class=content><span class=sampledata>4 4 1<br />
1 2 10<br />
2 4 10<br />
1 3 1<br />
3 4 100<br />
</span></div><h2>Sample Output</h2>
			<div class=content><span class=sampledata>1<br />
<br />
</span></div><h2>HINT</h2>
			<div class=content><p>K是1; 更新道路3->4使得从３到４的时间由１００减少到０. 最新最短路经是1->3->4,总用时<br />
为１单位.<br />
N<=10000</p></div><h2>Source</h2>
			<div class=content><p><a href='problemset.html?search=Gold'>Gold</a></p></div><center>[<a href='submitpage.php?id=1579'>Submit</a>][<a href='problemstatus.php?id=1579'>Status</a>][<a href='bbs.php?id=1579'>Discuss</a>]</center>﻿<br>

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